1. Field of the Invention
The present invention relates in general to a method suitable for monitoring the corrosion resistance and fouling condition of copper-alloy condenser tubes, through which seawater or estuary water typically flows, and more particularly to a method of maintaining the condition of the inner surfaces of the condenser tubes such that their corrosion resistance and heat transfer rate are optimized.
2. Discussion of the Prior Art and its Problems
Copper-alloy condenser tubes of a condenser which uses seawater (this term being interpreted to include water of estuary or bay) as a coolant have been conventionally maintained by (a) protecting the inner surfaces against corrosion, and (b) preventing deposition or accumulation of various suspended matters and corrosion products on the inner surfaces of the tubes, and thus avoiding the deterioration of heat transfer characteristics of the tubes. Described more specifically, it has been found extremely effective to inject ferrous ions in the form of ferrous sulfate into the coolant for increasing the corrosion resistance of the condenser tubes, and to pass sponge balls through the condenser tubes for cleaning the inner surface of the tubes to remove the deposited matters.
While the corrosion resistance of the condenser tubes is remarkably improved by a protective film of ferric hydroxide formed of ferrous ions injected in the form of ferrous sulfate, for example, it is also known that such a protective film will reduce the heat transfer characteristics of the condenser tubes. On the other hand, although cleaning the condenser tubes with sponge balls enhances the heat transfer of the tubes, it may also cause a decline in the corrosion resistance of the tubes if the protective film on the inner tube surface is excessively removed by the sponge-ball cleaning. Thus, there is a general recognition that the ferrous-ion injection and the sponge-ball cleaning are not satisfactorily stable and reliable for maintaining required corrosion resistance and heat transfer characteristics of the condenser tubes. In light of the above drawbacks, it has been proposed to inject ferrous ions and introduce sponge balls into the condenser tubes according to a program which is predetermined based on laboratory tests or field tests, so as to satisfy the two requirements, i.e., corrosion resistance and heat transfer rate of the condenser tubes. The program to carry out the ferrous-ion injection and sponge-ball cleaning is modified or revised as needed, based on the results of periodic inspection of the condenser tubes.
However, the nature of the cooling seawater is not kept constant during the service of the condenser. More particularly, the conditions of the seawater such as degree of pollution, condition of marine life, and concentration of slimes or sludges may change from time to time. Accordingly, the depth of a protective film resulting from the injection of a given amount of ferrous sulfate and the amount of foreign matter deposited after each sponge-ball cleaning may differ depending upon the changing conditions of the seawater introduced into the condenser tubes. Therefore, a continuous operation of a condenser with predetermined constant rate of ferrous-ion injection and sponge-ball cleaning is not considered a proper way to maintain the condenser tubes in the optimum conditions from the standpoint of corrosion resistance and heat transfer characteristics. Excessive corrosion or deterioration of heat transfer rate of the condenser tubes may cause economical losses due to non-productive time necessary for replacement of the tubes, increased fuel cost due to reduced thermal efficiency, and other undesirable factors that lead to lowering the operating efficience of a plant in which the condenser is installed.
Such economical losses due to corrosion or deteriorated heat transfer characteristics of the condenser tubes have been increasingly experienced in the industry because of a recent growing tendency toward expansion of capacity of power plants, or continuous operation of nuclear power plants. In order to overcome these drawbacks a method is provided for monitoring the corrosion resistance and heat transfer characteristics of condenser tubes, in order to control the injection of ferrous ions and the introduction of sponge-balls in response to information obtained by the monitoring, to optimize the anti-corrosion and heat transfer characteristics of the condenser tubes.